Torque limiting device



Filed April 18, 1958 June 28, 1960 E. cHAPoux TORQUE LIMITING DEVICE 2 Sheets-Sheet 1 fZa June 28, 1960 E. cHAPoUx 2,942,441

TORQUE LIMITING DEVICE Filed April 18, 1958 2 Sheets-Sheet 2 fdoua ra (,l/ POV/f A fl-armLy United States Patent 2,942,441 'roRQUE LmmNG DEVICE Edouard Chapoux, Paris, France, assignor to Induii S.A.l

de participations, Geneva, Switzerland, a firm of Swit- Torque devices of conventional types are hardly accurate or faithful .and their adjustment is a diicult matter. l

My invention has for its object an arrangement for limiting the torque transmitted to a drivenrmember by a driving member, said arrangement showing none of the prior drawbacks while its design is furthermore very simple. j Y Y According to my invention, there is provided for coupling two such members at least one yielding blade housed in vone of the latter and the free endV of which engagesv acm surface rigid with the other member, in a manner such that the blade may bend as a function of the torque to b e transmitted so as to disengage the cam and. to break the kinematic connection between the driving and Vdriven members when the sag of the blade has reached a predetermined value.V

It is a known fact that the sag assumed by a blade housed in its support vwhen subjected to a predeterg minedstress is reversely proportional to its momentum of inertiav and is proportional to the thirdpower of the length separating the point of application of the stress from the cross-section in which the blade is fitted. v l

By causing the member such as a rotary .shaft `which receives or transmits the torque which is tobe limited to act on blade of predetermined characteristics, the arrangement is such that Vsaid, shaft `is' releasedby the blade when the latter has reachedV a sag 4whichfis also of a predetermined Value "and it kis `thereforeY possible to limit very simply the torque transmitted to said' shaft or received by the latter. L v Y .Y A s Furthermore, 4through a suitable .modication of the length separating the point of application of the stress acting on the blade from the cross-section'thereofl which is held in its housing, it is possible to adjust as desired the value of the stress for which the kinematic connection between the driving member Vand the drivenrnember law defining the ytorque for which the blade assumes "a" predetermined sag as a function of the distance separating the point of application ofthe torque from the cross-V section of the said blade whichy is engaged by the housing. My improved device may lalso include means allowing a compensation of the play appearing rbetween its differentfelements and ensuring an auxiliary adjustment.V

Thel torque limiting `device forming theobject of my invention is intended for various applications and in particular it may be used to considerable advantage with dynamometric tools, such asscrew-drivers and the like.

I have illustrated by way of example, in the accompanying drawings, various embodiments of my improvedv device, together withmodilications thereof. In said drawings:

I Evbeing the modulus of elasticity of the blade and Iv its momentum of inertia with reference to the bending axis.'

Y 4sectional areagatvAl It is ,thensuicieng'ifuitjsi 5 IFig. 1 is a diagrammatic showing illustrating the ing of a blade tted through one of itsends. Y Y

Fig. 2 is a Ygraph showing Vthe intensity of the force required for bending by a predetermined amount a blade, a cross-section of which Vis set in a housing as a function of the operative length of said blade. Pig. 3 isal longitudinal sectional'view of aiirst embodiment of the invention.

Fig. 4 isa sectional view thereof through line IV-TV ofFig'.3. l e f f, f

Fig. 5 is a sectional view through line V-V of Fig. 3,

bendis assumed to occupy in Fig. 4'. p

Fig. 6 is a longitudinal sectional view of a rnr dification of the embodiment illustrated in Figs. 3 to Y5.

ligs. 7 and Sgare partial views on Va largerscale, respectively in sectional view land in plan view, showing means for locking the adjustingscx'ew. l

Fig. V9 is a Amodification of Fig. 8. Fig. 10 is a partial longitudinal sectional view showing two modifications of the cam. ,n

y It is a well-known fact that when an elastic blade l housed inside a support 2,'isv subjected to a stress P directed perpendicularly to its axis and applied at a distance ll fromY the Vcross-section sv through` which the blade is'housed, the sag f assumed by said blade under the action ofthe stress lP maybe calculated by the formula: f :A n

Assuming the sag has a constant value, the preceding relationship mayjbe written: Y f

i L P=l t and, if it is also -assum that the blade has a uniforrii y cross-section@ Q Y y .Pfr

1tY therefore Apossible to modify the stress produca-gjl a predetermined bending of the blade through a zmodifi-V cation of il, whichis the distance separatingl the point of application of the force lfrom `the cross-section of the?- i blade YengagedA by its housing.

' lt is also possible to dene the of a blade having a uniform ,cross-'section as in suchV a c`aseand Ias illustrated by the graph of Fig. 24, the curves f=constant 'extend asymptotically with reference to theL axis of ordinates which .is that giving the values of/the bladeV having a constant cross-section on the one hand- .It'is l'possible to'select among the various curves f2jthe usefulrangesPl, P2 corresponding on one V of curves fto the values vl1 andlz whichdeiine the'points A1 aud.AZ yfor a blade having the' predetermined crossv yI-"atented June 28, 1960 the cam occupying a position'dilerent from that which it law of variation of.,A the momentum Yofinertia of the cross-section of the blade asa function ofl so that -P may be a linear functionl of I,- if f is'assumed to beconstant. lt is thuspossible-to makethe adjustment ofthe Yforce or stress P easier when the value'Y of theV latter is somewhat considerable, since such an adjustment would not be an Yeasy matter in the case This graphs-shows curves f1', Yf2 corresponding a@ desired, to obtain .a linear variation of P=f(l) to make I vary.

The arrangement illustrated in Fig. 3 is adapted to limit the torque `transmitted by the shank of a dynamometric screw-driver to its head. It includes a blade 1 fitted inside a support 2 housed inside the cylindrical body 3 and heldin position by a threaded plug 4. The support 2 engages the shoulder 3a formed inside the front end of the body 3. Through :the support 2, there extends the shank 5 of a screw 6' the outer end 7 of which` is revolubly carried inside a bearing 8 fitted in the body 3, the blade 1 passing through the opening 3a of said bearing, which bearing is wide enough to allow the blade to bend freely.

, Inside the' cylindrical `body 3 Vis mounted a slider 9 fitted over the screw 6 as provided by itstaped bore 9a. Said slider is slotted at 9b to `allow the blade 1 to slide through -it under slight friction conditions. It is assumed in the present case that the blade has a constant Cross-section. It is possible to shift the slider 9 longitudinallyI inside the body 3through the agency of a control knob 10 carried by the screw'6. This leads consequently to -a modificationY in the length separating the free end of the blade from the actual section s which is housed at the point at which the blade passes out of the slider.

The outer `end of the body 3 contains a bearing 11 screwed into the said end of the body 3 and engaging a shoulder 3b formed inside the latter. Said bearing 11 carries revolubly a shaft 12 held in position inside the bearing 11 through the agency of the nut 13. Said shaft 12 is integral with the shank of a screw-driver, while the head of the latter, which is not illustrated, is rigid with the body 3. l

At its inner end 12a, the shaft 12 carries a cam 14 which is locked in position by a nut 14n threadedly engaging said end 12a ofthe shaft. This cam (Figs. 4 and S) includes two diametrically opposed bosses 15; adapted toengagethe free end la of the blade 1.

As illustrated in Fig. 5, when thecam 14 exerts through one of its bosses 15 a stress l? on the blade 1, the latter bends until the torque exerted by the shaft gives the blade a suicient bend for the boss 15 to move past said blade. The torque is then equal tothe product PXI', r being the distance separating the @axis of the shaft from the apex of the boss and P the force exerted on the blade.

When the boss 15 has thus moved beyond the blade, the kinematic connection between .the shank and the head of the screw-driver is broken. This leads to a release showing that it is no longer possible to act on the tool.

The shifting of the slider 9 modifies the value of the force P for which the desired sag is reached and which The value of this torque may be defined by the position assumed by the slider inside the casing or `again by the angular setting of the control knob 10. This position may be accurately measured for instance through the agency of a Vernier which leads to a highly accurate adjustment.

In the preceding disclosure, it has been Iassumed that the blade Awas moving under the action of the cam 14 tangentially with reference to the latter, so that it cannot move away yfrom the cam in the direction of the arrow F of Fig. 5. In order that the blade may actually move in` this tangential direction, an adjusting screw 16 engaged by the back of the blade is carried byk an extension 8b of the bearing 8. Said srew allows furthermore cutting out the clearance produced by the wear of the different parts and also providing a highly accurate complementary adjustment defining the value of the limit torque allowed while leaving a greater degree of freedom forthe blade in the direction of the arrow F.

'Fig 6 shows a bladef 1 the cross-,sectionof which is variable and is such as will provide a linear relationship are of particular advantage.

between the limit torque allowed and the length separating the point of application of the force P from the crosssection s through which the blade is housed.

Since the modification in length of said blade is obtained through a shifting of the slider, the modification in the cross-section of the blade is obtained by acting in a single direction on the size of the blade, which direction in the present case extends in the plane of the draw ing while the thickness of the blade remains constant `and is equal to the breadth of the slot 9b of the slider. The blade engages also an abutment formed by the screw 16 as in the preceding example.

In all cases, it is essential for the screw 16 tobe locked on the member carrying it in an elicient manner and in an accurately dened position.

It is possible to resort to this end to any conventional means, but the locking means illustrated in Figs. 7 and 8 In said figures, the screw 16 is provided centrally with a tapped opening 16a the pitch of 4which is preferably different from that of the outer thread on the screw. It is also provided in its outer end with a recess 16b the walls of which are provided with radial slots 16e.

The recess 16h carries a locking spring 17 including a shank 17a extending through one of the slots 16C and having its tail end 17b fitted inside an opening 18 formed inthe extension 8b of the bearing 8. Said extension is provided with a plurality of such openings 18 so as to provide a sufficient range of adjustment and it isfurtherimore provided with a recessed section 8c inside which the spring shank 17a is carried outside the projecting section of the screw 16. The spring 17 is in fact held in position by a screw 19 engaging the tapped opening 16a..

Instead of anchoring openings 18, it is possible to provide anchoring notches 20 or 21 as illustrated in Fig. 9. A The arrangement which has just been described may be simplified by cutting out the slider 9 and its adjusting screw 6, the adjustment of the limit torque being obtained then merely through the screw 16.

It is possible to provide the cam 14 with a number of bosses which is different from two and it is also possible to provide a plurality of blades such as 1.

Figure lO illustrates such a modification provided with a plurality of blades 1. In this case, the shaft `llZteIminates with `a plate 22 inside which is revolubly tted the end 7 of the screw 6 serving for the adjustment of the slider 9.

Various means may be resorted to for urging the plate 22 against the blades 1.

As illustrated in the lower part of Fig l0, the plate 22 may be provided with bosses 23 between which are fitted the terminal sections 24 of the corresponding blades, the length of said sections Z4 being defined in a manner such that the blades move past the `plate for a predetermined value of their sag. The bosses may as well be formed by balls 25 as illustrated in the upper part of Fig. 10, said balls being held inside corresponding recesses 25a of the plate by a covering plate 26 and projecting by a value equal to the length of the sections 24 beyond the ends of the blades.

The outer surface of the plate 22 abuts against a nut Z7 screwed into the wall of the body 3 and held in position by a set screw 28 extending through a bore 27a in the flange of the nut and screwed into a tapped opening 29 in the body 3. A number of balls 27a and holes 29 may be provided so as to allow compensation of play and further adjustment.

Obviously, the use of my improved arrangement is by no Vmeans limited to the operation of toolsand it may be used in any type of transmission while its etects are by no means limited to the breaking of a kinematic connection between two parts and itmay as-well engage or release any type of mechanism such as a safety mechanism for instance.

What I claim is:

l. A torque-limiting device comprising a hollow cylindrical body including a cover at each end, a shaft rotatably carried inside one of said covers and including a terminal section projecting slightly into said body, a flat yielding blade fitted in the other of said covers and extending freely inside the body up to a point in transverse registery with the terminal section of the shaft, a cam element rigid with the shaft and adapted to be operatively engaged by the free end of said blade registering with the terminal section of the shaft to allow said blade to transmit a torque between the body and the shaft while bending said blade until the blade being shifted onto the point of the cam outline furthest removed from the axis of the shaft for a predetermined maximum torque moves off the cam and releases the shaft, a stop cooperating with the outer surface of the blade and holding the latter in a position tangent with reference to the path followed by the outermost point of the cam element, and means for adjusting the location of the stop radially with reference to said path.

2. A torque-limiting device comprising a hollow cylindrical body including a cover at each end, a shaft rotatably carried inside one of said covers and including a terminal section projecting slightly into said body, a flat yielding blade fitted in the other of said covers and extending freely inside the body up to a point in transverse registry with the terminal section of the shaft, a cam element rigid with the shaft, and adapted to be operatively engaged by the free end of said blade registering with the terminal section of the shaft to allow said blade to transmit a torque between the body and the shaft while bending said blade until the blade being shifted onto the point of the cam outline furthest removed from the axis of the shaft for a predetermined maximum torque moves olf the cam and releases the shaft, an adjustable stop cooperating with the outer surface of the blade and bending the latter tangentially with reference to the path of the outermost point of the cam surface.

3. A torque-limiting device comprising a hollow cylndrical body including a cover at each end, a shaft rotatably carried inside one of said covers and including a terminal section projecting slightly into said body, a fiat yielding blade fitted in the other of said covers and extending freely inside the body up to a point in transverse registry with the terminal section of the shaft, a cam element lrigid with the shaft, and adapted to be operatively engaged by the free end of said blade registering with the terminal section of the shaft to allow said blade to transmit a torque between the body and the shaft while bending said blade until the blade being shifted onto the point of the cam outline furthest removed from the axis of the shaft for a predetermined maximum torque moves off the cam and releases the shaft, `an intermediate support carried slidingly inside the hollow body and provided with a perforation freely engaged by the blade, means for adjusting the location of said intermediate support longitudinally of the blade, an extension of said support extending alongside the blade outside` the latter and provided with a threaded hole facing the terminal section of the shaft, a screw adjustably fitted in the `threaded hole of said extension and cooperating with yielding blade fitted in the other of said covers and extending freely inside the body up to a point in transverse registry with the terminal section of the shaft, a cam element rigid with the shaft, and adapted to be operatively engaged by the free end of said blade registering with the terminal section of the shaft toy allow said blade to transmit a torque between the body and the shaft while bending said blade until the blade being shifted onto the point of the cam outline futhest removed from the axis of the shaft for a predetermined maximum torque moves off the cam and releases the shaft, an intermediate support carried slidingly inside the hollow body and provided with a perforation freely engaged by the blade, means for adjusting the location of said intermediate support longitudinally of the blade, anfextension of said support extending alongside the blade and provided with a threaded hole facing the terminal sections of the shaft and blade, a screw adjustably tted in the threaded hole of said extension and cooperating with the outer surface of the blade near its free end to bend the latter tangentially with reference to the cam surface, said screw being provided with a cylindrical coaxial recess in its head, an annular spring housed inside said recess and including a shank extending through the wall in the screw recess, a set screw holding the annular spring inside said recess coaxially therewith and means rigid with the extension of the intermediate support, in which means the shank of the spring is anchored.

5. A torque-limiting device comprising a hollow cylindrical body including a cover at each end, a shaft rotatably carried inside one of said covers and including a terminal section projecting slightly into said body, a flat yielding blade fitted in the other of said covers and extending freely inside the body up to a point in transverse registry with the terminal section ofthe shaft, a cam element rigid with the shaft, and adapted to be operatively engaged by the free end of said blade registering with the terminal section of the shaft to allow said blade to transmit a torque between the body and the shaft while bending said blade until the blade being shifted onto the point of the cam outline furthest removed from the axis of the shaft for a predetermined maximum torque moves off the cam `and releases the shaft, an intermediate support carried slidingly. inside the hollow body and provided with a perforation freely engaged by the blade, means for adjusting the location of said intermediate support longi-v tudinally of the blade, an extension of said support extending alongside the blade and provided with a threaded hole facing the terminal section of the shaft, a screw adjustably fitted in the threaded hole of said extension and cooperating with the outer surface of the blade near its free end to bend the latter tangentially with reference to the cam surface, said screw being provided with a cylindrical coaxial recess in its head, an Iannular spring housed inside said recess and including a shank extending through the wall in the screw recess, a set screw holding the annular spring inside the said recess coaxially therewith, the pitch of said screw being different from that of the first-mentioned adjustable screw, and means rigid with the extension of the intermediate support, in which means the shank of the spring is anchored.

References Cited in the le of this patent UNITED STATES PATENTS Siesel May 4, 1948 

